An antibacterial enzyme present in saliva and tears is called
- A.ribozyme
- B.lipase
- C.lysozyme
- D.isomerase
Correct answer
Explanation
The correct answer is C, lysozyme. Lysozyme kills bacteria by breaking down their cell walls, and it is found in saliva, tears and mucus.
Lysozyme attacks peptidoglycan, the main material of the bacterial cell wall, by splitting the bonds between its sugar units; the weakened cell then bursts. Gram-positive bacteria, whose walls are thick peptidoglycan, are most easily affected. Alexander Fleming discovered lysozyme in 1922, a few years before penicillin. It is part of the body's innate, non-specific defence, along with skin, stomach acid and mucus, and also occurs in egg white and breast milk.
A is wrong because a ribozyme is an RNA molecule that acts as a catalyst, not an antibacterial enzyme of tears.
B is wrong because lipase is a digestive enzyme that breaks fats into fatty acids and glycerol.
D is wrong because an isomerase converts a molecule into its isomer and has no antibacterial role.
Exam tip: salivary amylase (ptyalin) digests starch; lysozyme in saliva and tears kills bacteria; both were key Fleming-era finds of body defence.
Practice Questions
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- A.nickel
- B.iron
- C.tin
- D.aluminium
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Bronze is an alloy of copper and tin, usually about 88 parts copper to 12 parts tin. Adding tin makes copper harder, stronger and easier to cast, and bronze also resists corrosion well.
Read the full explanation →Which one of the following instruments is used for measuring moisture content of air?
- A.Hydrometer
- B.Hygrometer
- C.Hypsometer
- D.Pycnometer
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A hygrometer measures humidity, that is, the amount of water vapour or moisture in the air. The name comes from the Greek "hygros", meaning wet.
Read the full explanation →Which one of the following elements is present in the green pigment of leaves?
- A.Magnesium
- B.Iron
- C.Calcium
- D.Copper
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The green pigment of leaves is chlorophyll, and a magnesium atom sits at the centre of every chlorophyll molecule.
Read the full explanation →Consider the following actions :
1. Detection of car crash/collision which results in the deployment of airbags almost instantaneously
2. Detection of accidental free fall of a laptop towards the ground which results in the immediate turning off of the hard drive
3. Detection of the tilt of the smartphone which results in the rotation of display between portrait and landscape mode
In how many of the above actions is the function of accelerometer required?
- A.Only one
- B.Only two
- C.All three
- D.None
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Read the full explanation →Consider the following statements :
1. Carbon fibres are used in the manufacture of components used in automobiles and aircrafts.
2. Carbon fibres once used cannot be recycled.
Which of the statements given above is/are correct?
- A.1 only
- B.2 only
- C.Both 1 and 2
- D.Neither 1 nor 2
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Carbon fibre is widely used in cars and aircraft for its strength and low weight, and it can be recovered and recycled.
Read the full explanation →